I was sending a file through a form, and after using a form with multipart/form-data, server-side I had the File objects in req.files.

This gave me some information, like the path, name, size, type and so on:

{
  logo: File {
    size: 121920,
    path: '/var/folders/tn/h8lfq1sj7c33c0p30qgkd3mw0000gn/T/upload_b9e85b7cf989482a1760d82b77fd555a',
    name: 'Screen Shot 2021-06-07 at 21.40.29.png',
    type: 'image/png',
    hash: null,
    lastModifiedDate: 2021-06-07T22:20:50.150Z,
//...
  }
}

Notice the temp file path does not have an extension.

If you user the name server-side, no problem. But I wanted to change it and use my own naming conventions, so I needed just the file extension.

To get it, you can do 2 things: parse the file name, with

const path = require('path')
path.extname(req.files.logo.name) //.png

which does not require any 3rd party library.

Or you can use the mime-types package and look at the MIME type:

const mime = require('mime-types')
mime.extension('text/plain') //txt
mime.extension('image/png') //png

Lessons in this unit:

0:	Introduction
1:	How to check if a file exists in Node.js
2:	How to create an empty file in Node.js
3:	How to get the names of all the files in a folder in Node
4:	How to get the last updated date of a file using Node.js
5:	How to remove a file with Node.js
6:	How to write a JSON object to file in Node.js
7:	How to empty a folder in Node.js
8:	Working with file descriptors in Node
9:	Node File Paths
10:	Node file stats
11:	Working with folders in Node
12:	How to use the Node.js fs module with async/await
13:	How to get the current folder in Node
14:	▶︎ How to get the file extension in Node.js from the MIME type
15:	How to get the file extension in Node.js
16:	How to list files in a folder in Node
17:	How to mass rename files in Node.js
18:	Node.js get all files in a folder recursively
19:	Incrementing multiple folders numbers at once using Node.js
20:	Save some text to a file in Node.js